The present invention relates to pressure-sensitive adhesive constructions, and more particularly, to multilayer pressure-sensitive adhesive constructions which exhibit both good adhesion and good convertibility.
A conventional pressure-sensitive adhesive (PSA) label construction comprises a laminate of a facestock, a pressure-sensitive adhesive layer, and a coated release liner. The facestock may comprise any of a variety of materials, but is typically formed from paper or plastic films. The release liner provides a backing from which the facestock and the pressure-sensitive adhesive are peeled away just prior to label application. The surface of the release liner often consists of paper coated with a release layer of silicone.
Pressure-sensitive adhesive tape and label constructions are usually manufactured as a continuous roll in various widths, and are then processed to form finished product consisting of commercially useful labels or tape rolls. Such processing, known as converting, often involves cutting all or part of the bulk laminate roll. For example, one common converting operation in label manufacture is die cutting and matrix stripping, which involves precision cutting through the facestock and adhesive layers up to but not through the release surface, thereby cutting outlines of the labels, and then pulling away the surrounding matrix to leave only the individual labels on the release liner. Other converting operations may include butt cutting, guillotining, hole punching, slitting, and printing.
The cost of converting the bulk laminate PSA construction into the finished product depends in large part on the speed in which the converting processes can be carried out. The faster the PSA construction can be converted, the lower the cost of the finished product. While most of the current narrow-web converting presses operate at speeds of less than 152 meters per minute (500 ft/min), newer modern wide-web converting presses are designed to be operated at speeds of as high as 244 meters per minute (800 ft/min) or greater, and it is desirable to manufacture PSA constructions compatible with this converting speed.
It has been discovered that all layers of the laminate have some effect on converting speed, and much work has been directed at optimizing the facestock and release surfaces for faster converting. For example, increasing matrix stripping speed generally increases stripping force, which often results in matrix breaks which force press shutdown. This problem may be avoided by the use of higher strength facestocks, which convert better than low strength facestocks at a variety of converting speeds.
The adhesive layer, however, has been the greatest limiting factor with respect to the speed of converting bulk laminates into finished product. It is desirable to have an adhesive layer with good flow properties that can adhere to a wide variety of substrates. However, adhesive compositions which are formulated to have these properties do not always convert well, oftentimes sticking to the cutting dies, smearing on the matrix and label edges, and interfering with the precision cutting, or otherwise slowing down the converting process.
In addition, adhesive layers may also impact the matrix stripping operations which follow die cutting, causing breaks in the matrix if the converting press is run at too high a speed. To avoid these matrix breaks, press operators are often forced to slow the converting presses to well below the optimal operating speed.
Thus, it is desirable to provide pressure-sensitive adhesive constructions which feature adhesive layers which show good adhesion to a wide variety of substrates of varying roughness, and which are also compatible with optimal converting performance.
The present invention is directed toward pressure-sensitive adhesive constructions which show good adhesion to a wide variety of substrates, and which also convert well.
In one aspect of the present invention, there is provided a pressure-sensitive adhesive construction with a facestock. A first adhesive layer is on the facestock. The first adhesive layer comprises a first adhesive composition with a first glass transition temperature. The first adhesive composition may be either an acrylic based or a rubber-based adhesive and may include a first organic additive.
A second adhesive layer is on the first adhesive layer. The second adhesive layer comprises a second adhesive composition with a second glass transition temperature which is lower than the first glass transition temperature. The second adhesive composition may be either an acrylic based or a rubber-based pressure-sensitive adhesive and may include a second organic additive. A release liner may be on the second adhesive layer
In one preferred embodiment, the first glass transition temperature is about 10xc2x0 C. to about 50xc2x0 C. higher than the second glass transition temperature. More preferably, the first glass transition temperature is about 15xc2x0 C. to about 35xc2x0 C. higher than the second glass transition temperature.
If a rubber-based adhesive layer is present in the first and/or second layer, it may contain polymeric components selected from a group consisting of block copolymers of styrene-butadiene-styrene, styrene-isoprene-styrene, styrene-butadiene, styrene-isoprene, multibranched styrene-butadiene, and multibranched styrene isoprene, individually, or in combinations thereof. If an acrylic based adhesive composition is present in the first or second adhesive layer, it may consist in part of polymers formed from the polymerization of at least one alkyl acrylate monomer, where the alkyl group contains from about four to about twelve carbon atoms, in an amount from about 35% to about 95% by weight of the polymer.
When rubber-based adhesive composition are used, the organic additive in the adhesive composition includes a tackifier present in a concentration by weight of about 40-90%. Moreover, the organic additive might also include a plasticizer, present in the first adhesive composition and/or second adhesive composition in concentration of about 1-30% by weight.
In another aspect of the present invention, there is provided a pressure-sensitive adhesive construction with a facestock. A first layer is on the facestock. The first layer has a first polymeric composition with a first glass transition temperature. The first polymeric composition also has a first storage modulus, and a first tangent delta. A second layer is on the first layer. The second layer has a second polymeric composition with a second glass transition temperature. The second polymeric composition is a pressure-sensitive adhesive composition.
The first layer has mechanical loss such that it contributes to the peel force. The first layer also has a high storage modulus at die-cutting frequency so as to prevent smear. Thus, in a preferred embodiment of this aspect of the invention, the first storage modulus at a frequency of 104 radians per second at 20xc2x0 C. is greater than about 3xc3x97108 dynes/cm2, and the first tangent delta at 102 radians per second at 20xc2x0 C. is greater than about 0.5. In this embodiment, the first layer may comprise a pressure-sensitive adhesive layer, or it may comprise an adhesive layer which does not exhibit pressure-sensitive adhesive properties.